I found the first "spiral" pretty easy, but the second one I made sure to give a little more gusto, and by the end my legs were burning pretty good. Next time I'll have a better idea of how deep to go - really it's best not to hold back at all and just go for full burn, over and over.

Heart rate was interesting - the peak of each interval was pretty close, but how far down I managed to recover progressively increased until by the last few I was barely recovering at all before the next interval.

Oh and there are some surprise intervals at the end of the second "spiral". Spoiler alert.

I loved the workout - but the footage wasn't that great on this one, got pretty repetitive. They've definitely upped their game in their more recent videos.